Natural ventilation effectively reduces hyperhydricity in shoot cultures of Aloe polyphylla Schonland ex Pillans

An investigation into the role of ventilation to reduce hyperhydricity in tissue cultures of Aloe polyphylla Schonland ex Pillans revealed that gaseous exchange between the in-vitro atmosphere and the outside environment is an essential prerequisite for controlling this disorder. In closed culture vessels, hyperhydricity affected as much as 84% of the newly-formed shoots on media gelled with gelrite. The leaves of hyperhydric shoots had a bright green colour, smooth epidermis and large, open stomata. Gaseous exchange was promoted by using modified lids with a hole covered with polyester or cotton mesh. In ventilated cultures, hyperhydricity was completely eliminated irrespective of the type of gelling agent used. Natural ventilation was further advantageous for the microplants in terms of leaf chlorophyll content as well as the deposition of epicuticular wax, indicating the onset of mechanisms that regulate water loss from the explants. Although culture ventilation was negatively correlated to the regeneration rate and shoot growth, it has the potential to control the appearance of abnormal phenotypes and can be easily adopted for routine A. polyphylla propagation in vitro.